An ion beam etching (hereinafter, also referred to as IBE) process has been used, for example, in multiple steps in production of magnetic sensors used for hard disk drives, which are magnetic recording media. Shapes of magnetic head elements of a magnetic sensor are three-dimensional structures. The shapes of the elements provided in a substrate surface after the etching process have to be highly uniform. To make the shapes of the element uniform, the etching process is performed with the substrate being rotated when the shapes of the elements are mirror symmetric, whereas the etching process is performed with the substrate fixed in any direction when the shapes of the elements are not mirror symmetric. Elements with non-mirror symmetric shapes can be formed by utilizing the facts that the shapes of the elements obtained after the etching are determined by the incident angle of the ion beam on the substrate surface, and that the incident angle of the ion beam is determined by the substrate tilt angle during the process.
To form elements with asymmetric shapes in a step of producing magnetic heads, a substrate held static may be processed with a relatively low incident angle of about 20 degrees in some cases (hereinafter, this condition is referred to as a low-angle-incident static condition). When the IBE process is performed on a substrate held static, the shapes of the elements may be nonuniform within the substrate surface. This nonuniformity is attributable to the fact that when a substrate is tilted in an in-plane direction, the distance from the ion source varies depending on the position on the substrate surface, and hence the incident angle of an ion beam emitted from the ion source varies depending on the position on the substrate surface. This nonuniformity is also attributable to the angle of deviation of the ion beam due to the plasma density distribution inside the ion source.
The nonuniformity in the substrate surface under the low-angle-incident static condition also depends on the energy of the ion beam. Especially, an ion beam of an acceleration voltage of 400 V or higher enables a highly uniform process even under the low-angle-incident static condition, because such an ion beam has a high moving speed of the ions and hence has a high rectilinearity of the ions. However, with an ion beam of an acceleration voltage of less than 400 V, the etching amounts and the shapes of the elements in the substrate surface under the low-angle-incident static condition become nonuniform, because the moving speed is low and the path of the ions is deviated.
Apparatuses have been proposed for obtaining elements with uniform shapes in a substrate surface. An IBE apparatus of Patent Document 1 scans a substrate surface with a spot-shaped ion beam by two-dimensionally moving an ion source with a small aperture diameter and a substrate. An IBE apparatus of Patent Document 2 scans a substrate surface with a slit-shaped ion beam by moving a substrate in a direction perpendicular to a long axis of a rectangular ion source. In this IBE apparatus, a flat-plate shutter for forming the slit-shaped ion beam is provided between the ion source and the substrate to control the incident angle of the ion beam on the substrate surface with respect to the moving direction of the substrate.